1. Field of the Invention
The present invention is related to forming wire bonds between the contact pads on semiconductor devices and individual lead frame fingers of a lead frame.
More specifically, the present invention is related to the apparatus and method of forming improved wire bonds between the contact pads on semiconductor devices and individual lead fingers of a lead frame using one or more independently actuated lead penetrating bond head lead clamps or a fixed bond head clamp which may be either penetrating or not during the wire bonding process.
2. State of the Art
Well known types of semiconductor chip devices are connected to a component known as lead frames and subsequently encapsulated in plastic for use in a wide variety of applications. The lead frame is typically formed from a single continuous sheet of metal, typically by metal stamping operations. The lead frame includes an outer supporting frame, and may include a central semiconductor chip supporting pad and a plurality of lead fingers, each lead finger having, in turn, a terminal bonding portion near the central chip supporting pad. Ultimately, the outer supporting frame of the lead frame is removed after the wire bonds between the contact pads of the semiconductor chip device and the lead fingers have been made and after the encapsulation of the semiconductor chip and portion of the lead fingers.
Since the lead frames are formed continuously using stamping operations, they are typically continuously rolled on a suitable reel and provided for use. Such reeling operations of the lead frames cause the lead frames to have induced stresses and deformations therein leading to lead frames exhibiting longitudinal curvature and transverse curvature, as well as deformation of the individual leads of the lead frame. Such lead frame curvature and any attendant deformation of the leads and lead frame cause problems in the formation of reliable wire bonds with the contact pads of semiconductor devices and the individual lead fingers of the lead frame. Particularly, problems arise when the size of the semiconductor is decreased, the number of contact pads on the semiconductor device is increased, and the number of lead fingers on the lead frame is increased. In order to form the desired connections between the bond pads of a semiconductor device and a lead frame during the wire bonding process, the lead fingers of the lead frame must be immobilized in a known, predetermined location with respect to the semiconductor device.
Typical apparatus and methods for forming the wire bonds between the contact pads on semiconductor devices and the lead fingers of lead frames are illustrated in U.S. Pat. Nos. 4,361,261, 4,527,730, 4,600,138, 4,653,681, 4,765,531, and 5,465,899. However, such apparatus and methods do not address the problem of deformed lead frames and their effect on the wire bonds.
Typically, the deformation of the lead frames and its effect on the quality of wire bonds have been dealt with through the use of clamps on portions of the lead frames during the wire bonding operation. In U.S. Pat. No. 4,434,347 a circular fixed clamp is used to retain the lead fingers of the lead frame during the wire bonding operation. A spring loaded electrode is used to heat the end of the lead finger to help improve bonding of the wire.
In U.S. Pat. No. 5,322,207 a fixed clamp is used to retain the lead frame during the automated wire bonding process for connecting the bond pads of a semiconductor device to lead fingers of a lead frame.
In U.S. Pat. No. 5,307,978 a fixed clamp is illustrated for use in an apparatus and method for orienting bonding sites of a lead frame at a bonding station of an automatic wire bonder.
In U.S. Pat. No. 5,035,034 a hold-down clamp having a multi-fingered interchangeable insert for wire bonding semiconductor lead frames is illustrated. The circular clamp insert includes a plurality of individual fingers used to bias a lead finger of a lead frame in the wire bonding process to provide a better wire bond by attempting to immobilize the lead frame during bonding operations.
In U.S. Pat. No. 3,685,137 the jaws of a lead frame clamp are used to force the lead fingers of a lead frame into a fixed position during the wire bonding process.
In U.S. Pat. No. 4,821,945 a method and apparatus for the single lead automated clamping and bonding of lead fingers of lead frames are illustrated. However, such apparatus and method are used to replace the fixed clamp during such wire bonding. Additionally, the individual clamp is concentrically located with respect to the wire bonding apparatus and must rotate therearound during wire bonding operations.
While such prior art apparatus and methods have been directed in attempting to solve the problems of forming reliable wire bonds between the contact pads of semiconductor devices and lead fingers of lead frames, they have not been as successful because none of the prior art clamps effectively immobilizes a lead finger during wire bonding operations as the clamps merely engage the surface of a lead finger, if properly positioned thereon.
The present invention is directed to an improved wire bonding apparatus and method for forming wire bonds between semiconductor devices and lead frames by immobilizing the lead finger during the wire bonding process.